A mammoth seven-alarm fire tore through six buildings in a Somerville neighborhood today, displacing up to 40 people from their homes but causing no apparent serious injuries, fire officials said.

Two firefighters were taken to the hospital, Somerville fire chief Kevin Kelleher said, with one suffering a knee injury and the other respiratory problems.

“All the residents we know of are accounted for,” he said. “We’re just very fortunate that there are no serious injuries we know of at this point.”

Firefighters were called to Calvin Street just after 6 a.m., Kelleher said. Four buildings were already on fire when they arrived.

Smoke filled the street and brought traffic in the area to a standstill. Residents in this tightly-knit block were seen in the street, some with pets in their arms. Fire officials also pushed back everyone when over fears one of the triple-deckers could collapse due to the heavy fire damage.

The Red Cross is on scene to help those who were displaced.

Somerville police, Somerville firefighters and the state fire marshal’s office are working to determine how the fire started.